Stabilizers for peracids



United States Patent Ofiice 3,168,554 Patented Feb. 2, 1965 3,i68,55d S'EAiiiLlZEi-EG FUR Beniarnin Phillips, Qharleston, Sans el W. 'llinsley, South Charleston, and Paul Starcher, tilharleston, W. Va, assignors to Union Qarhide Corporation, a corporation of New York No Drawing. Filed May 26, 196%, Ser. No. 31,797 4- Claims. (Cl. Z6t3-5@2) This invention relates to a method for stabilizing peracids. In one aspect this invention relates to a method for stabilizing peracetic acid. In another aspect this invention relates to the use of a pyiidine-Z-methanol, certain phosphorus compounds, and a mixture comprising certain phosphorus compound and a pyridine-Z-rnethanol, as stabilizers for peracids.

Peracetic acid, for example, has become quite important commercially within the last ten years, principally as a reagent for converting olefins into the corresponding epoxides. However, in situations where it is necessary to store peracetic acid for a period of time, the tendency of the acid to slowly decompose on storage, even at room temperature, can be a decided disadvantage. After fourteen weeks storage at room temperature, commercial grade, unstabilized peracetic acid has been observed to go from a peracetic acid content of about 40 percent to about 13 percent. This is obviously an important economic factor, and practical means for retarding this decomposition will have great utility.

It is believed that the decomposition reactions which occur on storage include the following free-radical reactions:

(H) II II orr oo-0H orno o' on (III) 0 zornii-oca om 200,

(IV) z-on moi Hi0 /0i These, and other iree-radical reactions, probably all take place. There isevidence that decomposition is catalyzed by very small amounts (traces) of heavy metals. Other foreign materials, such as dust, have also been found to increase the rate of decomposition; The trace amounts of foreign materials that are picked up when peracetic acid is prepared in metal equipment, or even in glass-lined equipment, is sufficient to reduce the stability of the acid. 7

In accordance with this invention, it has been discovered that the addition of minor amounts of certain substances to peracids greatly improves the storage stability of said peracids. It is likely that the stabilization is effected by the ability of said substances to suppress the catalytic power of the contaminants that promote decomposition. However, the exact mechanism by which the stabilization is effected is unknown, and it is to be understood that this invention is not limited by or restricted to any theory of action expressed herein.

The substances which have been found to have a stabilizing effect on peracids fall into four general groups.

t t M Group 1) comprises the pyridine-Z-methanols having A- orrzorr the formula: wherein A represents a member selected from the group consisting of hydrogen atoms and X, and X represents a member selected from the group consisting of COOH and CH OH radicals, provided that only one A represents an X.

It has been discovered that when certain phosphorus compounds are employed as stabilizers for peracids in combination with a pyridine-Z-methanol, as defined above, novel synergistic eifects'are obtained. Thus, Group (2) is a mixture comprising a pyridine-2-methanol as defined above and a member selected from the group consisting of the phosphoric acids, the alkali metal salts of the phosphoric acids, the alkyl acid esters of the phosphoric acids, the alkali metal salts of the alkyl acid esters of the phosphoric acids, and the alkaline earth metal salts of the allcyl acid esters of the phosphoric acids.

Group (3) comprises the long chain alkyl acid esters of orthophosphoric acid having the formula:

wherein each R individually represents a member selected from the group consisting of hydrogen atoms and alkyl radicals having from 1 to 20 carbon atoms, provided that at least one R represents a long chain alkyl radical having from 12 to 20 carbon atoms. a

Group (4) comprises the long chain alkyl acid esters of pyrophosphoric acid having the formula:

wherein each R individually represents a member selected from the group consisting of hydrogen atoms and .alkyl radicals having from 1 to 20 carbon atoms, provided that at least one R represents a long chain alkyl radical having from 12 to 20 carbon atoms.

It is an object of thisinvention to provide a method for the stabilization of peracids. It is a further object of this invention toprovide a. method for the stabilization of peracetic acid. It is a still furtherjobjectof this invention to provide a method for the stabilization of peracids which comprises adding to said acid a minor amount of a pyridine-Z-methanol. A further object of this invention is to provide a method for the stabilization of peracids which comprises adding to said acid a mixture comprising a minor amount of pyridine-Z-methanol and a minor amount of a phosphorus compound selected from the group consisting of the phosphoric acids, the alkali metal salts of the phosphoric acids, the alkyl acid esters of the phosphoric acids, the alkali metal salts of the alkyl acid esters of the phosphoric acids and the alkalinete arth metal salts of the alkyl acid esters of the phosphoric acids. A still further object of this invention is to provide a method tetrapolyphosphoric acid, octapolyphosphoric acid,

areassa for the stabilization of peracids which comprises adding to said acid minor amounts of a long chain alkyl acid ester of orthophosphoric acid. A further object of this invention is to provide a method for the stabilization of peracids which comprises adding to said acid minor amounts of a long chain alkyl acid ester of pyrophosphoric acid. Other objects of the invention will become apparent to those skilled in the art upon examination of the detailed description which follows:

The pyridine-Z-methanols which are effective as stabilizers for peracids are represented by the formula:

A \N/ omen (I) wherein A represents a member selected from the group consisting of hydrogen atoms and X, and X represents a member selected from the group consisting of COOH and CH OH radicals, provided that only one A represents an X. Thus, the Group (1) stabilizers are the pyridine-2-methanols that have either a COOH radical or a CH OH radical on one of the open positions on the ring, that is, on either the 3, 4, 5 or 6 position on the ring. Exemplary members include pyridine-2,6-dimethlanol; pyridine-Z-methanol-6-carboxylic acid; pyridine-2,4-

dimethanol; pyridine-2-methanol-4-carboxylic acid; pyridine-2,5-dimethanol; pyridine-Z-methanol 3 carboxylic acid, and the like. The preferred pyridine-Z-methanols are those in which X is located on the 6 position on the ring, and therefore have the formula:

X N CH OH wherein X is a member selected from the group consisting of CH OH and COH radicals.

The stabilizers of Group (2) are mixtures comprising a pyridine-Z-methanol as defined above and a member selected from one of the following five classes of phosphorus compounds:

(a) The phosphoric acids, (b) The flkali metal salts of the phosphoric acids, (0) The alkyl acid esters of the phosphoric acids, (d) The alkali metal salts of the alkyl acid esters of the phosphoric acids, and (e) The alkaline earth metal salts of the alkyl acid esters of the phosphoric acids.

(a) The term the phosphoric acids refers to the acids resulting from the reaction of phosphorus pentoxide (P 0 with water. The formation of these acids is illustrated by the following equations:

H O+P O 2HPO (metaphosphoric acid) 2H O+P O H P O (pyrophosphoric acid) 3H O+P O 2H PO (orthophosphoric acid) Also included are the polymetaphosphoric acids and the polyphosphoric acids. Exemplary members include metaphosphoric acid, orthophosphoric acid, pyrophosphoric acid, tetrametaphosphoric acid, pentametaphosphoric acid, hexametaphosphoric acid, tripolyphosphoric acid, and the like.

(b) The alkali metal salts of the phosphoric acids consists of the salts of orthophosphoric acid, pyrophosphoric acid, the polymetaphosphoric acids and the polyphosphoric acids, wherein at least one hydrogen atom has been replaced by an alkali metal Examples include sodium dihydrogen phosphate, lithium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium hexametaphosphate, tetrasodium pyrophosphate, sodium tetrapolyphos phoric acid, disodium octapolyphosphoric acid, and the like. Preferred are the sodium salts of ortho-, pyro-, the polymeta-, and the polyphosphoric acids.

(c) The alkyl acid esters of the phosphoric acids are the partially esterified alkyl esters of orthophosphoric acid, pyrophosphoric acid and the polyphosphoric acids wherein said alkyl groups have from 1 to carbon atoms. The partially esterified phosphoric acids may be prepared by the reaction of an alcohol with phosphorus pentoxide as, for example,

Other ratios of alcohol to phosphorus pentoxide will yield derivatives of meta-, ortho-, and poly-phosphoric acids.

It will be apparent to one skilled in the art that an alkyl acid ester, or partially esterified alkyl ester, will have at least one acidic hydrogen atom in the molecule.

Therefore, an alkyl acid ester of one of the phosphoric acids will always have the group present in the molecule. Examples of the alkyl acid esters of the phosphoric acids that are contemplated by this invention include dimethyl dihydrogen pyrophosphate, dioctyl dihydrogen pyrophosphate, distearyl dihydrogen pyrophosphate, ethyl stearyl hydrogen orthophosphate, pentaoctyl dihydrogen pentapolyphosphate, diisopropyl hydrogen orthophosphate, and the like.

(d) The alkali metal salts or" partially esterified phosphoric acids are the partially or completely neutralized compounds of (0), wherein at least one of the acidic hydrogens has been replaced with sodium, potassium, lithium, or other alkali metal. The commercially available product Victawet having the empirical formula Na R (P O (R=2-ethyll1exyl) is of this type.

(e) The alkaline earth metal salts of the alkyl acid esters of the phosphoric aci s are the calcium, barium, strontium, magnesium, etc., salts of the alkyl acid esters as defined above. Particularly preferred are the calcium salts of the alkyl acid esters of the polyphosphoric acids, such as calcium pentaoctyl pentapolyphosphate.

In addition, this invention contemplates two classes of phosphorus compounds that are useful as stabilizers for peracids. The first class is the long chain alkyl acid esters of orthophosphoric acid having the formula:

wherein each R individually represents a member selected from the group consisting of hydrogen atoms and alkyl radicals having from 1 to 20 carbon atoms, provided that at least one R represents a long chain alkyl radical having from 12 to 20 carbon atoms. Exemplary long chain alkyl acid esters of orthophosphoric acid include ethyl stearyl hydrogen orthophosphate, distearyl hydrogen orthophosphate, dilauryl hydrogen orthophosphate, methyl cetyl hydrogen orthophosphatc, dimyristyl hydrogen orthophosphate, stearyl dihydrogen orthophosphate, di-

wherein each R individually represents a member selected from the group consisting of hydrogen atoms and alkyl radicals having from 1 to 20 carbon atoms, provided that at least one R represents a long chain allryl radical having from 12 to 20 carbon atoms. Examples of long chain .alkyl acid esters of pyrophosphoric acid include clistearyl dihydrogen pyrophosphate, methyl stearyl dihydrogen pyrophosphate, dilauryl dihydrogen pyrophosphate, myristyl trihydrogen pyrophosphate, butyl dicetyl hydrogen pyrophosphate, dieicosyl dihydrogen pyrophosphate, and the like. The preferred long chain alkyl acid esters of pyrophosphoric acid are those in which the long chain alkyl radicals are stearyl radicals.

The amount of stabilizer employed is not necessarily critical. The beneficial effects are observed in stabilizer concentrations as low as 0.0005 percent, based on weight of peracid, and lower, up to concentrations as high as 5.0 percent based on weight of peracid, and higher. The

preferred concentration range is from about 0.05 percent to about 1.0 percent, based on weight of peracid.

Where the stabilizer is a mixture comprising a pyridine- Z-methanol and one of the phosphorus compounds falling in Group (2), the concentrations are not critical, and both-components individually can be employed in concentrations varying from about 0.0005 percent to about 5 percent, based on Weight of peracid. The preferred concentration of both components individually is from about 0.02 percent to about 1 percent, based on the weight .of peracid.

The stabilizers provided by this invention are effective as stabilizers for organic peracids such as peracetic acid, perbutyr ic acid, perbenzoic acid, monoperphthalic acid, and particularly for the unsubstituted aliphatic monocarboxylic peracids having from 2 to 4- carbon atoms, such as peracetic acid, perpropionic acid and perbutyric acid. It is preferred that these stabilizers be employed with peracetic acid or perpropionic acid. ferred is peracetic acid.

The stabilizers are effective over the whole useful temperature range of the peracids with which they are employed. This corresponds generally to a range of from about -50 C. to about 150 C. The stabilizers are also effective at sub-atmospheric, super-atmospheric and atmospheric pressure.

The beneficial effects of the stabilizers are found at all useful concentrations of peracids in any of the common solvents. Thus, the stabilizers are effective at concentrations of peracids varying from about 5 percent to about 90 percent by weight, based on total Weight of the solution. The stabilizers are particularly useful in peracid concentrations of from about percent to about 70 percent, based on total weight of the solution. Highly preferred concentrations of peracid are from about 30 percent to. about60 percent, based on total weight of solution.

The solvents that can be employed to dissolve the eracids include acetic acid, ro ionic acid, butyric acid,

water, acetone, dioxane, diethyl ether, chloroform, ben: zene, toluene, ethyl acetate, butyl acetate, hydrogen peroxide, mixtures thereor", and the like.

The following non-limiting examples illustrate the effectiveness of the stabilizers provided by this invention as stabilizers for peracetic acid.

Highly prein acetic acid. The containers used were 4-ounce glassstoppered bottles for the room temperature (23 C.) tests, and 30 x 200 mm. test tubes connected to 8-inch air condensers for the elevated temperature (SO- C.) tests. Because of the sensitivity of the peracetic acid stability to small amounts of impurities (i.c., even dust), all of the glassware was carefully cleaned with soap and water, cleaning solution, distilled water and finally with reagent grade acetic acid.

Approximately 60 ml. of peracetic acid of about 30-40 percent (by weight) concentration was used in each test. To this amount of peracid solution was added the stabilizer and the samples were stoppered and allowed to stand at room temperature in the dark (bench cabinet). For the higher temperatures, the test tubes equipped with air condensers were immersed in a waterbath and kept in diffused light. intervals (a Week or longer for room temperature studies down to a few hours in the 80 C. studies and analyzed for peracetic acid content. The pipettes used for sam pling ere carefully cleaned before use and between sampling diiferent bottles. The final result in each case is reported in the tables which follow.

The peracetic acid content can be determined, for example, by introducing 1-1.5 grams of the sample into a flask containing 60 milliliters of 50 Weight percent aqueous sulfuric acid solution and five milliliters of a Examples 1-10 These examples illustrate the synergistic effect obtained when using a pyridine-2-n1ethanol in a mixture with the phosphorus compounds falling in Group (2).

Storage Percent Peracetic Acid Stabilizers (percent Ex. based on Weight of Tem- Controlperacctic acid) Time pera- Initial Final No ture, Stabili- 0. zer

1---" 0.1% pyridine-2, 13.75 50 43. 7 21.8 13. 5

(i-dimethanol. days 2 0.1% pyridine/2, 13.75 50 43. 7 26. 6 13. 5

0-dirnethanol days plus 0.1% sodinm hexarnstar phosphate. 3-.. 0.1% pyridinoZ, 13.75 50 43. 7 22. 4 13. 5

G-dimcthanol days plus 0.1% dioctyl dihydro gen pyrophosphate. 4---" 0.1% pyridine-2, 13.75 50 43. 7 22. '1 13. 5

ddirnothanol clays plus 0.1% distearyl dihydrogen pyrophcsphate. i i 5 0.1% distearyl 18.75 50 43.7 18. 5 13. 5

dihydrcgen days pyrophosphato. 6 0.1% pyridine-2, 44 23 43. 7 8.1 1. 1

fi dimethanol. weeks 7 0.1% pyridine-2, 44 23 43. 7 29.0 1.1

G-dimethanol v. eeks plus 0.1% so (lium hexametaphosphate. 8 0.l%scdimnhexa- 69.9 80 46.4 7.3 1.7

metaphosphato. hours 9 0.1% pyridine-2, (54.5 80 40. 4 16.9 4.7

G-dimcthanol. hours 7 10--.- 0.1% pyridine-2, 6-1.5 80 40.4 17.3 4.7

G-dimethanol hours plus 0.1% sodium hcxamotaphosphate.

Samples were withdrawn at regular (7 Examples 11-21 These ex nples further illustrate the efiectiveness of the pyrrdme-Z-rnethanols in mixtures With phosphorus compounds as stabilizers for pcracetic acid.

Storage Percent Peracetic Acid Stabilizers (percent Ex. based on weight of Tern- Control peracettc acid) Time pera- Initial Final No 'ture, Stabili- C. zer

11. 0.1% pyridine-2,6- 14 50 43. 7 24. 7 14. 4

dimethanol. days 12 0.1% pyridine-2,6- 14 50 43. 7 32.3 14. 4

dimethanol plus days 0.1% sodium hexametaphospliate. 13. 0.1% pyridine-2,6- 44 80 46. 4 12.4 2. 2

dimethanol. hours 14 0.1% pyridine-Z- 44 80 46. 4 8. 3 2. 2

methanol-G- hours carboxylic acid. 15 0.1% pyridine-2,6- 64. 80 46. 4 16. 9 4. 7

dimethanol. hours 16- 0.1% pyridine-2,6- 64.5 80 46. 4 11. 2 4. 7

dimethanol plus hours 0.1% Vietawet 35B. 17 0.1% pyridine-2,6- 64.5 80 46. 4 12. 6 4 7 dimethanol plus hours 0.1% tetrasodium pyrophosphate. 18 0.1% pyridine-2,6- 64. 5 80 46. 4 18. 4 4 7 dim'ethanol plus hours 0.1% dioctyl dihydrogen pyrophosphate. 19- 0.1% pyridine2,6- 64. 5 80 46. 4 l7. 3 4. 7

dirnethanol plus hours 0.1% sodium hexametaphosphate. 20. 0.1% pyridine-2,6- 64. 5 80 46. 4 18. 4 4 7 dimethanol plus hours 0.1% distearyl dihydrogen pyrophosphate. 21---. 0.1% pyrid1n0-2,6- 64. 5 80 46. 4 13. 3 4 7 dirnethanol plus hours 0.1% ethyl stearyl hydrogen orthophosphate.

Examples 22-31 These experiments illustrate the effectiveness of the compounds falling in Groups (3) and (4) as stabilizers for pcracetic. acid.

Storage Percent Peracetic Acid Stabilizers (percent Ex. based on weight of Tem- Controlperacetic acid) Time pera- Initial Final N o tnre, Stabili- C. zcr

22.. 0.01% distearyl 14 23 41.5 24. O 13.95

dihydrogen weeks pyrophosphate. 23 0.1% distearyl di- 14 23 41.5 34. 3 13. 95

hydrogen pyroweeks phosphate. 24 0.5% distearyl di- 14 23 41.5 30. 9 13. 95

hydrogen pyroweeks phosphate. 25.--. 1.0% distearyl di- 14 23 41. 5 33.3 13. 95

hydrogen pyroweeks phosphate. 26- 2.5% distearyl dl- 14 23 41.5 25.9 13.95

hydrogen pyroweeks phosphate. 27---. 5.0% disteai'yl di- 14 23 41.5 20.9 13.95

hydrogen pyroweeks phosphate. 28.--. 0.01% ethyl 14 23 41 5 26. 6 13. 95

stearyl weeks hydrogen orthophosphate. 29" 0.1% ethyl 14 23 41.5 30.5 13. 95

stearyl hyweeks drogen orthophosphate. Y 30 0.5% ethyl stearyl 14 23 41. 5 26. 55 13. 95

hydrogen orthoweeks phosphate. 31- 1.0% ethyl stearyl 14 23 41. 5 27. 15 13. 95

hydrogen orthoweeks phosphate.

What is claimed is:

1. A stabilized organic peracid selected from the group consisting of perbenzoic acid, monoperphthalic acid, and the unsubstituted aliphatic monocarboxylic peracids having from 2 to 4 carbon atoms, wherein said organic peracid contains a small amount of a pyridine-Z-rnethanol of the formula:

wherein A represents a member of the group consisting of hydrogen and X, and wherein X represents a member selected from the group consisting of carboxylic acid groups and hydroxymethyl groups, provided that only one A represents an X.

2. A stabilized aliphatic monocarboxylic peracid having from 2 to 4 carbon atoms, which contains from 0.0005 Weight percent to 5 Weight percent, based on Weight of said aliphatic monocarboxylic peracid, of a pyridine-2- methanol of the formula:

wherein A represents a member selected from the group consisting of hydrogen atoms and X, and wherein X represents a member selected from the group consisting of carboxylic acid groups and hydroxymethyl groups, provided that only one A represents an X.

4. A stabilized peracetic acid which contains from 0.0005 Weight percent to 5 weight percent, based on weight of said peracetic acid, of pyridine-2,6-dirnethanol.

References Cited in the file of this patent UNITED STATES PATENTS Greenspan et a1. Apr. 1, 1952 Greenspan et al. Sept. 2, 1952 Greenspan et al. Jan. 6, 1953 Dunn et a1 Sept. 20, 1960 Banfield July 10, 1962 Dunlop et al Sept. 11, 1962 OTHER REFERENCES Phillips et al.: Journal or Organic Chemistry, vol. 23, pages 1823-1826, January 21, 1959. 

1. A STABILIZED ORGANIC PERACID SELECTED FROM THE GROUP CONSISTING OF PERBENZOIC ACID, MONOPERPHTHALIC ACID, AND THE UNSUBSTITUTED ALIPHATIC MONOCARBOXYLIC PERACIDS HAVING FROM 2 TO 4 CARBON ATOMS, WHEREIN SAID ORGANIC PERACID CONTAINS A SMALL AMOUNT OF A PYRIDINE-2-METHANOL OF THE FORMULA: 